Rubber vulcanization | Article about Rubber vulcanization by The Free Dictionary Rubber vulcanization | Article about Rubber vulcanization by The Free Dictionary vulcanization (vŭl'kənəzā`shən), treatment of rubber rubber, any solid substance that upon vulcanization becomes elastic; the term includes natural rubber (caoutchouc) and synthetic rubber. The term elastomer is sometimes used to designate synthetic rubber only and is sometimes extended to include caoutchouc as well. ..... Click the link for more information. to give it certain qualities, e.g., strength, elasticity, and resistance to solvents, and to render it impervious to moderate heat and cold. Chemically, the process involves the formation of cross-linkages between the polymer chains of the rubber's molecules. Vulcanization is accomplished usually by a process invented by Charles Goodyear Goodyear, Charles, 1800–1860, American inventor, b. New Haven, Conn., originator of vulcanized rubber. He failed in his earlier business ventures and was in jail for debt when he began his experiments with rubber, searching for a way to prevent it from sticking and melting .....

Click the link for more information. in 1839, involving combination with sulfur and heating. A method of cold vulcanization (treating rubber with a bath or vapors of a sulfur compound) was developed by Alexander Parkes in 1846. Rubber for almost all ordinary purposes is vulcanized; exceptions are rubber cement, crepe-rubber soles, and adhesive tape. Hard rubber is vulcanized rubber in which 30% to 50% of sulfur has been mixed before heating; soft rubber contains usually less than 5% of sulfur. After the sulfur and rubber (and usually an organic accelerator, e.g., an aniline compound, to shorten the time or lower the heat necessary for vulcanization) are mixed, the compound is usually placed in molds and subjected to heat and pressure. The heat may be applied directly by steam, by steam-heated molds, by hot air, or by hot water. Vulcanization can also be accomplished with certain peroxides, gamma radiation, and several other organic compounds.

The finished product is not sticky like raw rubber, does not harden with cold or soften much except with great heat, is elastic, springing back into shape when deformed instead of remaining deformed as unvulcanized rubber does, is highly resistant to abrasion and to gasoline and most chemicals, and is a good insulator against electricity and heat. Many synthetic rubbers undergo processes of vulcanization, some of which are similar to that applied to natural rubber. The invention of vulcanization made possible the wide use of rubber and aided the development of such industries as the automobile industry. Vulcanization a technological process in rubber production in which raw rubber is made into cured rubber. Vulcanization increases the durability, hardness, elasticity, and heat and cold resistance of raw rubber and lowers its degree of swelling and solubility in organic solvents. The essence of vulcanization is the joining of the linear macromolecules of raw rubber into a single, “sewn” system—the so-called vulcanization network. As a result of vulcanization, cross-links are formed between the macromolecules; the number and structure of the cross-links depend on the method of vulcanization.

During vulcanization certain properties of the vulcanized mixture change with time, but they pass through a maximum or minimum rather than change constantly. The degree of vulcanization at which the rubber achieves the best combination of various physical and mechanical properties is called the optimal vulcanization. Mixtures of raw rubber with various substances that ensure the necessary useful qualities of the cured rubber (fillers such as carbon black, chalk, and kaolin; softeners; and preservatives) are usually vulcanized. In most instances, raw rubber for general use (natural rubber, butadiene, or butadiene-styrene) is vulcanized by heating it with elemental sulfur to 140°-160° C (sulfur vulcanization). The intermolecular cross-links that form are made up of one or several sulfur atoms. If 0.5 to 5 percent sulfur is added to the raw rubber, a soft vulcanizate (for automotive inner tubes and tire casings, balls, tubes, and so on) is formed. The addition of 30 to 50 percent sulfur leads to the formation of a hard, inelastic substance, ebonite.

Sulfur vulcanization can be accelerated by the addition of small quantities of organic compounds—so-called vulcanization accelerators such as kaptaks or thiuram. These substances are fully active only in the presence of metal oxides (most often zinc oxide), which are activators. In industry sulfur vulcanization is accomplished by heating the articles being vulcanized in molds under high pressure or in the form of unformed articles (in “free” shape) in boilers, autoclaves, individual vulcanizers, or apparatus for continuous vulcanization. In these devices heating is done by steam, air, superheated water, electricity, or high-frequency current. The forms are usually put between the heated plates of a hydraulic press. Vulcanization with sulfur was discovered by C. Goodyear (USA, 1839) and T. Hancock (Great Britain, 1843). To vulcanize raw rubber for special uses, organic peroxides (such as benzoyl peroxide), synthetic resins (for example, phenol-formaldehyde), and nitro and diazo compounds are used. The conditions of vulcanization are the same as for sulfur vulcanization.

Vulcanization is also possible under the action of ionizing radiation (gamma radiation from radioactive cobalt) and streams of fast electrons (radiation vulcanization). Methods of sulfurless and radiation vulcanization allow the production of rubbers with high thermal and chemical resistance. REFERENCES vulcanization | rubber manufacturing | Britannica.com rubber manufacturing latex Vulcanization, chemical process by which the physical properties of natural or synthetic rubber are improved; finished rubber has higher tensile strength and resistance to swelling and abrasion, and is elastic over a greater range of temperatures. In its simplest form, vulcanization is brought about by heating rubber with sulfur . Charles Goodyear, undated engraving. Library of Congress, Washington, D.C. (Digital File Number: cph 3a09814) The process was discovered in 1839 by the U.S. inventor Charles Goodyear , who also noted the important function of certain additional substances in the process. Such a material, called an accelerator , causes vulcanization to proceed more rapidly or at lower temperatures.

The reactions between rubber and sulfur are not fully understood, but in the product, the sulfur is not simply dissolved or dispersed in the rubber; it is chemically combined, mostly in the form of cross-links, or bridges, between the long-chain molecules. In modern practice, temperatures of about 140°–180° C are employed, and in addition to sulfur and accelerators, carbon black or zinc oxide is usually added, not merely as an extender, but to improve further the qualities of the rubber. Anti-oxidants are also commonly included to retard deterioration caused by oxygen and ozone. Certain synthetic rubbers are not vulcanized by sulfur but give satisfactory products upon similar treatment with metal oxides or organic peroxides. Learn More in these related articles: Rubber and Vulcanisation - OpenLearn - Open University Rubber and Vulcanisation Rubber and Vulcanisation Updated Wednesday 9th August 2006 In the Rough Science programme Lost at Sea, the Rough Scientists Ellen and Kathy are given the task of making a life-jacket. They decide to use kapok to fill the jacket but need to make it waterproof so the contents don’t get wet.

Zanzibar has a rich variety of plants and on one of her trips inland Ellen spotted some rubber trees – so they know they can get some fresh latex, but the problem is how to make this cover the life-jacket to give a strong but flexible barrier. The answer is Vulcanisation, precipitating out the rubber particles, mixing them with sulphur and heating the treated material over a fire. To find out more about the process of vulcanisation read the following extract from the second level OU course Our Chemical Environment (ST240). Copyright: Production team Chains of natural rubber are very long and have few if any cross-links, and so the material is a thermoplastic, becoming soft and sticky in the summer and hard and brittle in the winter. These disadvantages were overcome in 1839 by a discovery made accidentally by Charles Goodyear in Woburn, Massachusetts. The story goes that after many years of experimenting, he had spilt or accidentally placed a mixture of rubber, sulfur and lead oxide on a hot stove. The rubber was no longer sticky but had been converted to a tough, elastic substance stable to heat and cold. It also did not dissolve in the solvents that dissolved natural rubber.

He had invented the process now known as vulcanization. Vulcanization is a chemical reaction between sulfur and rubber resulting in cross-links being formed between the rubber polymer chains. Notice here: Copyright: Used with permission that there are double bonds present in the polymer molecule. You should remember that double bonds provide a major route to the formation of polymers, so it should not be a surprise to find that these double bonds can serve to provide covalent links between the chains. Copyright: Production team We can form covalent bonds between the polymer molecules, and if we do this the material will become much more rigid because the chains are no longer free to move apart. The more cross-links between chains, the more rigid the rubber until eventually the polymer is so cross-linked that it is no longer rubbery because there is no flexibility of the chains between the cross-links. Goodyear’s vulcanization process produces a controlled amount of cross-linking. The sulfur reacts with the double bonds and forms sulfur bridges as cross-links between the chains, resulting in a huge three-dimensional network as you can see here.

Copyright: Used with permission Charles Goodyear | Goodyear Corporate THE CHARLES GOODYEAR STORY Read about Goodyear’s namesake, Charles Goodyear, and the accidental discovery that lead to the vulcanization process. In midsummer of 1834, a bankrupt hardware merchant from Philadelphia, Charles Goodyear, walked into the New York retail store of the Roxbury India Rubber Co., America's first rubber manufacturer. He showed the store manager a new valve he had devised for rubber life preservers. The manager shook his head sadly. The company wasn’t in the market for valves now; it would be lucky to stay in business at all. He showed Goodyear why: rack on rack of rubber goods which had been melted to malodorous glue by the torrid weather. In the company's factory at Roxbury, Mass., he confided, thousands of melted rubber articles were being returned by outraged customers. The directors had met in the dead of night to bury $20,000 worth of stinking rejects in a pit. The “rubber fever” of the early 1830s had ended as suddenly as it had begun.

At first everybody had wanted things made of the new waterproof gum from Brazil, and factories had sprung up to meet the demand. Then abruptly the public had become fed up with the messy stuff which froze bone-hard in winter and turned glue-like in summer. Not one of the young rubber companies survived as long as five years. Investors lost millions. Rubber, everyone agreed, was through in America. Goodyear disappointedly pocketed the valve and took his first good look at rubber. He had played with bits of it as a child, but now, at 34, he experienced a sudden curiosity and wonder about this mysterious “gum elastic.” “There is probably no other inert substance,” he said later, “which so excites the mind.” Returning to Philadelphia, Goodyear was clapped into jail for debt. It was not his first sojourn there, nor his last. He asked his wife to bring him a batch of raw rubber and her rolling pin. Here, in his cell, Goodyear made his first rubber experiments, kneading and working the gum hour after hour.

If rubber was naturally adhesive, he reasoned, why couldn’t a dry powder be mixed in to absorb its stickiness — perhaps the talc-like magnesia powder sold in drugstores? Out of jail again, he tried, with promising results. He talked a boyhood friend into backing a modest venture. Charles, his wife and small daughters made up several hundred pairs of magnesia-dried rubber overshoes in their kitchen. But before he could market them summer came, and he watched his footwear sag into shapeless paste. Neighbors complained about Goodyear’s smelly gum, so he moved his experiments to New York. There a friend gave him a fourth-floor tenement bedroom for his “laboratory.” A brother-in-law came to his squalid quarters, lectured him about his hungry children, advised him that rubber was dead. “I am the man to bring it back,” said Goodyear. He was adding two drying agents to his rubber now, magnesia and quicklime, then boiling the mixture and getting a better product all the time. Impressed, a New York trade show awarded him a medal.

Goodyear lavished all the arts of decoration on his dingy samples, painted them, gilded them, embossed them. Running short of material one morning, he decided to re-use an old decorated sample and applied nitric acid to remove its bronze paint. The piece turned black, and Goodyear threw it away. A few days later he remembered that somehow the blackened scrap had felt different. He retrieved it from his trash can and found he was right. The nitric acid had done something to the rubber, made it almost as smooth and dry as cloth. This was better rubber than anyone had ever made before. A New York businessman advanced several thousand dollars to begin production. But the financial panic of 1837 promptly wiped out both the backer and the business. Destitute, Charles and his family camped in the abandoned rubber factory on Staten Island, living on fish he caught in the harbor. In time, Goodyear got new backing in Boston and again seesawed to momentary prosperity. His partners wangled a government contract for 150 mailbags, to be manufactured by the nitric-acid process.

After making the bags, Goodyear was so sure of himself that he stored them in a warm room and took the family away for a month’s vacation. When he returned, the mailbags melted. Underneath their “dry-as-cloth” surface lay the same old sticky gum. After five futile years, Goodyear was near rock bottom. Farmers around Woburn, Mass., where he now lived, gave his children milk and let them dig half-grown potatoes for food. The great discovery came in the winter of 1839. Goodyear was using sulphur in his experiments now. Although Goodyear himself has left the details in doubt, the most persistent story is that one February day he wandered into Woburn’s general store to show off his latest gum-and-sulphur formula. Snickers rose from the cracker-barrel forum, and the usually mild-mannered little inventor got excited, waved his sticky fistful of gum in the air. It flew from his fingers and landed on the sizzling-hot potbellied stove. When he bent to scrape it off, he found that instead of melting like molasses, it had charred like leather.

And around the charred area was a dry, springy brown rim — “gum elastic” still, but so remarkably altered that it was virtually a new substance. He had made weatherproof rubber. This discovery is often cited as one of history’s most celebrated “accidents.” Goodyear stoutly denied that. Like Newton’s falling apple, he maintained, the hot stove incident held meaning only for the man “whose mind was prepared to draw an inference.” That meant, he added simply, the one who had “applied himself most perseveringly to the subject.” The winter after Goodyear’s discovery was the blackest of his life. Dyspeptic and gout-racked, his health broken, he hobbled about his experiments on crutches. He knew now that heat and sulphur miraculously changed rubber. But how much heat, for how long? With endless patience he roasted bits of rubber in hot sand, toasted them like marshmallows, steamed them over the teakettle, pressed them between hot irons. When his long-suffering wife took her bread from the oven, he thrust in chunks of evil-smelling gum. At night he lay awake, afraid that he would die and the secret with him.

He pawned his watch and the household furniture. When even the dinnerware was gone, he made rubber dishes to eat from. Then the food was gone, too. That spring he went to Boston to look up friends, found none, was jailed for nonpayment of a $5 hotel bill, and came home to find his infant son dead. Unable to pay for a funeral, Goodyear hauled the little coffin to the graveyard in a borrowed wagon. Of the 12 Goodyear children, six died in infancy. At last he found that steam under pressure, applied for four to six hours at around 270 degrees Fahrenheit, gave him the most uniform results. He wrote his wealthy New York brother-in-law — who had once lectured him about his parental obligations — of his discovery. This time the brother-in-law, a textile manufacturer, was interested, for Charles told him that interwoven rubber threads would produce the fashionable puckered effect then much favored in men’s shirts. Two “shirred goods” factories were rushed into production and, on the ruffled shirtfronts of dandies, rubber rode to worldwide success.

As soon as he could, Goodyear disposed of the manufacturing interests — which might have made him a millionaire — and went back to his experiments. He wanted to make everything of rubber: banknotes, musical instruments, flags, jewelry, ship sails, even ships themselves. He had his portrait painted on rubber, his calling cards engraved on it, his autobiography printed on and bound in it. He wore rubber hats, vests, ties. Goodyear saw rubber as what we know it is today: the first and most versatile of the modern “plastics.” He perceived in it a “vegetable leather” that defied the elements, an “elastic metal,” a wood substitute that could be shaped in molds. Some of his ideas still turn up as “new” uses for rubber. Many food packagers, for example, now wrap their products in Pliofilm, a rubber-derived plastic; Goodyear suggested the same application in 1850. Rubber paint, car springs, ferryboat bumpers, wheelbarrow tires, inflatable life rafts, and “frogmen” suits are other recent innovations he described a century ago. Goodyear’s business deals, licensing manufacture under his scores of patents, were ridiculously bad.

Shirred-goods rights, for instance, went for royalty of three cents a yard; the licensees made $3 a yard. Against “patent pirates” Goodyear was forced to prosecute 32 infringement cases all the way to the U.S. Supreme Court. In one famous 1852 case, his advocate was no less a personage than Secretary of State Daniel Webster. Goodyear paid Webster $15,000 for temporarily doffing the robes of Cabinet office — the largest fee ever paid an American lawyer to that time. In a two-day speech Webster won a permanent injunction against further patent infringements. It made headlines, but it didn’t stop the piracy. Goodyear was slow in filing foreign patent applications. But he had sent samples of his heat-and-sulphur-treated gum to British rubber companies without revealing details. One sample was seen by famed English rubber pioneer Thomas Hancock, who had been trying for 20 years to make weatherproof rubber. Hancock noticed a yellowish sulphur “bloom” on the Goodyear sample’s surface. With that clue, he reinvented vulcanized rubber in 1843, four years after Goodyear.

By the time Goodyear applied for an English patent he found that Hancock had filed a few weeks earlier. Offered a half-share of the Hancock patent to drop his suit, Goodyear foolishly declined — and lost. A friend of Hancock named the contested process “vulcanization,” after Vulcan, the Roman god of fire. At the London and Paris world’s fairs of the 1850s, Goodyear installed great pavilions built entirely of rubber, floor to roof. When his French patent was canceled on a technicality and his French royalties stopped before he could pay his bills, he was seized by gendarmes and hustled off to a 16-day stay at his familiar “hotel” (as he called it) — debtors’ prison. There he received the Cross of the Legion of Honor, bestowed by Emperor Napoleon III. When he died, in 1860, he was $200,000 in debt. Eventually, however, accumulated royalties made his family comfortable. His son, Charles Jr., inherited something more precious — inventive talent — and later built a small fortune on shoemaking machinery.

Neither Goodyear nor his family was ever connected with the company named in his honor, today’s billion-dollar Goodyear Tire & Rubber Co., the world’s largest rubber business. Goodyear’s only direct descendant among modern companies is United States Rubber, which years ago absorbed a small company he once served as director. Today there is a cultivated rubber tree for every two human beings on earth. Three million tree “milkers” harvest the crop. The United States alone imports almost half of it, and synthesizes as much or more from petroleum. Nearly 300,000 Americans earn their livelihoods in rubber manufacturing. This year will produce $6 billion worth of products. The whole huge apparatus owes its existence to the invincible little fanatic who might have died a bitter man, but didn’t. “Life,” he wrote, “should not be estimated exclusively by the standard of dollars and cents. I am not disposed to complain that I have planted and others have gathered the fruits. A man has cause for regret only when he sows and no one reaps.” REPRINTED FROM THE JANUARY 1958 ISSUE OF READER'S DIGEST.

©1957 THE READER'S DIGEST ASSOCIATION, INC., PLEASANTVILLE, N.Y. 10570 PRINTED IN U.S.A. This reprint does not constitute an endorsement, implied or otherwise, by Reader's Digest. It may not be used in any way for advertising or promotional purposes without prior written permission of Reader's Digest. The reprint may not be sold by anyone other than Reader's Digest and no message, with the exception of the donor's name, may be imprinted on it. Portrait of Charles Goodyear by G.P.A. Healey. Charles Goodyear discovers the vulcanization process. Contact Us Please make sure you've entered valid information for all required fields. Note: All fields are required To: What is Vulcanized Rubber? (with pictures) What is Vulcanized Rubber? Originally Written By: R. Kayne Revised By: A. Joseph Edited By: L. S. Wynn Last Modified Date: 18 January 2017 Copyright Protected: These 10 facts about space will blow your mind Vulcanized rubber is a natural elastomer that has been made more durable by a biochemical process that cures the rubber.

During vulcanization, the milky latex from a rubber tree is combined with a curing ingredient — usually sulfur — and heated under pressure. This process, which was discovered by an American inventor named Charles Goodyear in 1839, made the rubber more stable, tougher and more resistant to heat, which made it more useful for industrial purposes and ideal for certain products. Its name comes from Vulcan, the Roman god of smiths. Making Rubber Stronger Before vulcanization was discovered, natural rubber could be coagulated with acid and made malleable so that it could be shaped and formed. At high temperatures, though, the rubber would become sticky or melt. At low temperatures, the rubber would become brittle. These qualities made this type of rubber impractical to use in industrial settings. Vulcanization chemically combines the rubber and sulfur. At high pressure and high temperatures, the sulfur atoms form links or bridges between long chains of the rubber molecules. This increases the rubber's strength and durability and reduces its stickiness. It also makes the rubber retain its elasticity at a much wider range of temperatures, making vulcanized rubber more useful for many purposes. Ad Discovery Goodyear had experimented with rubber for several years before discovering vulcanization.

A former hardware store owner who had no scientific training or knowledge of chemicals, Goodyear suffered financially and went into debt while looking for a way to make rubber more stable and durable. It is often said that his discovery was by accident after a mixture of sulfur and rubber gum splattered onto a hot stove and formed a hardened material. Goodyear, however, claimed that it was not accidental but rather the result of a series of experiments and observations. He sent samples of his cured rubber to British rubber plants. An Englishman named Thomas Hancock, who had been trying to make weatherproof rubber for 20 years, saw one of the samples and he noticed a telltale yellowish powdery residue — sulfur — on the surface of the sample. Hancock reinvented the process in 1843, four years after Goodyear. Goodyear obtained the United States patent for this process in 1844, but when he applied for the British patent, he found that Hancock had beaten him to it. The term "vulcanized rubber" did not come from Goodyear, but was coined by a friend of Hancock's. Applications Vulcanized rubber has come to be used to make a wide variety of products.

Among the most common of these are automobile tires, rubber seals and gaskets, transmission belts, shoe soles and hockey pucks. The Goodyear Tire and Rubber Company, a well-known manufacturer of automobile tires and other rubber products, was named in honor of Charles Goodyear, although there are no family connections. Ad Rubber Chemistry - How Rubber Works | HowStuffWorks How Rubber Works Getty Images What makes rubber so elastic? Like plastic, rubber is a polymer, which is a chain of repeating units called monomers. In rubber, the monomer is a carbon compound called isoprene that has two carbon-carbon double bonds. The latex fluid that seeps from rubber trees has many isoprene molecules. As the latex dries, the isoprene molecules crowd together and one isoprene molecule attacks a carbon-carbon double bond of a neighboring molecule. One of the double bonds breaks, and the electrons rearrange to form a bond between the two isoprene molecules. The process continues until you have a long strands of many isoprene molecules linked like a chain. These long strands are called polyisoprene polymer. Each polyisoprene molecule contains thousands of isoprene monomers.

As the drying continues, the polyisoprene strands stick together by forming electrostatic bonds, much like the attraction between opposite poles of two bar magnets . The attraction between these strands holds the rubber fibers together and allows them to stretch and to recover. Up Next How Kinesio Tape Works However, temperature changes can affect the electrostatic interactions between the polyisoprene strands in latex rubber. Hot temperatures reduce the interactions and make the rubber more fluid (sticky). Colder temperatures increase the interactions and make the rubber more solid (hard, brittle). In the early 1800s, several scientists and inventors set out to make rubber more durable. One famous inventor, Charles Goodyear, reasoned that you could reduce rubber's stickiness by mixing it with various dry powders. He experimented by combining talcum and other powders with rubber. In 1838, Goodyear met Nathaniel Hayward, who had made progress in treating rubber sheets with a solution of sulfur and turpentine and then drying them in the sun . Hayward's sun-dried rubber was harder and more durable, so he patented the process, which he called solarization. Goodyear purchased the patent rights to solarization and began experimenting with sulfur compounds.

By trial and error, the inventor mixed latex rubber with sulfur and lead oxide. Legend has it that some of the mixture fell onto a hot stove, and the resulting rubber was hard, flexible and durable. Goodyear's a­ccidental process eventually became known as vulcanization. He also found that changing the amount of sulfur changed the rubber's characteristics. The more sulfur used, the harder the rubber became. So what happens when rubber is vulcanized? When polyisoprene strands are heated with sulfur and lead oxide, the sulfur atoms attack the double bonds in the polyisoprene strands and bind to the carbon atoms. Sulfur atoms also can form bonds among themselves (disulfide bonds) and cross-link adjacent polyisoprene strands to form a netlike structure in the rubber. ­Thi­s cross-linking strengthens the polyisoprene to make it harder, flexible and more durable. As Goodyear found, the more sulfur used, the more cross-links can form, and the harder the rubber gets. Goodyear's vulcanization process involved combining latex rubber, sulfur and lead oxide in high-pressure steam for up to 6 hours to achieve the best results. Rubber Prince or Pauper?

Charles Goodyear was obsessed with rubber. He even experimented with it while he was confined to debtor's prison. After he invented vulcanization in 1839, he started making sheets of vulcanized rubber that could be used for clothing. Goodyear sent his products to Europe in hopes of enticing investors. English inventor and rubber pioneer Thomas Hancock was enticed. He figured out Goodyear's vulcanization process and hastily applied for an English patent before Goodyear. Ultimately, many other businesses infringed on Goodyear's patents, and he spent much of his fortune on litigation or on rubber experiments. He died impoverished in 1860. He'd probably be happy to know that the Goodyear Tire and Rubber Company was named in his honor. Untitled Document If you have come to this page from a search engine please click here for a full site map and access to all site pages Home > Chemistry, Technology & Conservation > Vulcanization The vulcanization of polyolefinic rubbers can be defined as the process by which the reaction between the polyolefin and sulphur results in greatly increased elastic properties of the polyolefin and the maintenance of these properties over a comparatively wide temperature range.

The term ‘vulcanization’ was proposed by Mr Brockedon to Thomas Hancock who took out the first patent for the process in 1843, although it is now universally accepted that the action of sulphur, lead oxide and heat on natural rubber to ‘cure’ it of its propensity to turn brittle when cold and sticky when hot was discovered by Charles Goodyear in 1839. Indeed, in the US the terms ‘cure’ and ‘curing’ tended to be used instead of ‘vulcanize’ and ‘vulcanizing’ and this has resulted in a number of problems and anachronisms which will be addressed later. It was rapidly established that, whilst the basic ingredients of a vulcanizing system were sulphur, a base oxide such as lead oxide or zinc oxide and heat, the last ranging today from about 120oC to 200oC, other chemicals could be added to the mix to speed up the process at any given temperature and even today new chemicals (called generically ‘accelerators’) are being brought into commercial use.

Apart from the obvious reason of getting a slice of an existing market the reasons tend to be threefold: To modify the vulcanization process in such a way as to make it more cost-effective. To modify the vulcanization chemistry and thereby obtain a product with improved performance characteristics. For environmental or ‘health & safety’ reasons. Because a rubber product can contain materials such as fillers and oils which are not part of the vulcanization process, it is the ratio of sulphur and accelerators to the rubber which is important in defining the type of vulcanising system so quantities are expressed not as %’s but as ‘parts by weight per hundred parts of rubber’ (pphr) or (phr). However, before considering actual quantities it is worth considering what happens during the vulcanization process. For close to a century after the discoveries of Goodyear and Hancock the argument raged as to what was the interaction between the rubber and sulphur.

As early as 1898 Ostromislenski (Ostromuisslenski) had proposed a combined chemical/physical theory of vulcanization whilst in 1902 Weber proposed a purely chemical one and in 1910 Ostwald opted for some sort of physical mixture or ‘alloy’ formation. Although the evidence for a chemical inter-reaction became overwhelming to most scientists there was still a bitter argument between the two sides at an international conference on vulcanization as late as 1939. The chemical structure of the natural rubber vulcanizate was finally resolved during the 1960’s and 70’s at the Malaysian Rubber Producers’ Research Association by studies of the reaction between sulphur and various accelerators with low molecular weight olefins which could be taken as models of the rubber olefinic unit. This work led to the conclusion that the polymer chains of an unvulcanized rubber were joined together (crosslinked) by sulphur bridges to give a three dimensional network and it was this which provided the increased elasticity of the vulcanized product.

The detailed picture was extremely complex, showing that the sulphur could initially attach itself to one of several carbons within the monomer unit and could then either remain there or undergo a chemical shift to another carbon atom. The length of the sulphur bridge was also variable, being 1, 2, 3 or even more sulphur atoms whilst the final complication was that the sulphur bridge might not have been formed between two adjacent polymer molecules but it could have looped back to the same polymer chain from whence it started. An understanding of these factors enabled some quantitative observations obtained almost a century ago to be understood. In the early days of vulcanization, before the introduction of modern accelerators but when the advantages of adding a little organic base were appreciated, trial and error had shown that around 2.5 pphr sulphur gave a good useful vulcanized rubber product and this came to be known as a conventional vulcanizate. This level of sulphur is used today, with around 0.5 pphr accelerator and what the model olefin studies, together with calculations of the crosslink density of the vulcanizate, showed is that it is not an efficient system.

The polysulphidic crosslinks and other non-crosslinking sulphur chemistry means that it needs about 12 sulphur atoms to produce one crosslink. If the levels of the ingredients are reversed to 0.5 pphr sulphur and 2.5 pphr then we have an efficient vulcanizate (EV) with only about 3 sulphurs required for each crosslink. Not surprisingly it is possible to design semi-EV systems between these two extremes. Zinc oxide is today the preferred inorganic base, usually added at around 5 pphr, although for applications where transparency is desired (baby feeding teats, medical tubing etc.) it can be as low as 1 pphr. Just because the terms conventional and efficient are used these should not be equated with ‘old’ and ‘new’ (better). The different systems give different properties to the vulcanizates at the same level of crosslinks and the system chosen will depend on the anticipated use of the product.

Many vulcanizing systems for rubbers using chemicals other than sulphur have been investigated over the last 150 years but very few exist commercially today and here we tend to move from the word ‘vulcanization’ to ‘cure’. The use of sulphur chloride ( 1846 - Parkes Process ) is called the sulphur chloride cure process and we also have peroxide cured rubbers. Cold vulcanization processes, such as the ubiquitous cycle repair patch, are called ‘cold cure’ processes. To add a further layer of complication, the chemicals which may be added to a rubber mix to effect vulcanization, including the accelerators, are collectively called curatives and the remains of these chemicals after vulcanization, cure residues. It should also be remembered that early stories of the preparation of ‘dry’ rubber from latex in South America involved the smoking over open fires of layers of rubber built up on paddles whilst smoking sheets of coagulated and semi-dried natural rubber is still practised today in eastern plantations and cooperatives. This process was familiar to the British as it mirrored that used to smoke or ‘cure’ fish.

Inevitably therefore the smoking process for rubber also became known as curing and for some time the two quite different meanings were used with much confusion. Eventually it became accepted that ‘curing’ only referred to the reaction with sulphur and the other process was called ‘smoking’. Making Rubber Stronger: How to Vulcanize Rubber Making Rubber Stronger: How to Vulcanize Rubber Washing Machine Vibration – How to Reduce it with a Rubber Mat Rubber is a polymer of isoprene that is formed with double bonds between each of the individual monomers (or units). In simple terms, one of these bonds is flexible and can allow the polymer to take up many shapes and sizes, which is what basically gives rubber its property of elasticity. But, that being the case, that flexible bond is also what makes rubber in its natural form somewhat imperfect (for example, perhaps natural rubber is too elastic for some applications), because if that bond were stronger, it would create a better material that could be more widely used. There is a process that can strengthen that bond called rubber vulcanization . This process involves heating natural sheet rubber and rubber products with sulfur, and it is a widely-used method for the creation of commercial rubber parts.

While the process on how to vulcanize rubber is in fact a complex one, it can be broken down into simpler terms for everyone to understand. Rubber supplies and parts are now generally vulcanized, unless they are made out of tire crumb in which case they are molded. Vulcanization was discovered accidentally by Charles Goodyear in 1839, and it involved altering the chemistry of the compound; it was named after Vulcan, the Roman god of fire. As stated previously, the molecular structure of rubber is that of a chain comprised of a very large amount of units of isoprene that are linked together with a double bond. Because of the free bond between the units, rubber is very flexible, perhaps too flexible for some commercial rubber applications. So, sulfur is introduced into the compound through intense heating, and the free bond is no longer free, creating a crosslink between chains. While this reduces natural rubber’s elasticity, it also makes for a substance that is far superior in its strength and resistance to abrasion and harsh conditions. It also makes the rubber non-stick and eliminates its thermoplastic nature, meaning that it will not return to its original shape after it cools.

In truth, there are other elements that can be used for this process, such as selenium or tellurium, but sulfur is by far the element of choice. It can then be processed into sheets or rolls, then cut or customized into products for both simple and specialized uses.

Making Rubber Stronger: How to Vulcanize Rubber Closed Cell Rubber - EPDM Patent EP2601249A1 - Process for recycling and de-vulcanizing rubber - Google Patents Process for recycling and de-vulcanizing rubber EP 2601249 A1 (text from WO2012017414A1 ) Abstract The process for recycling and de-vulcanizing vulcanized rubber comprises the steps of: grinding said rubber in a mill in order to shred it into particles having a size substantially comprised between 5 and 15 mm; introducing the particles in an initial section of a two- screw co-rotating extruder having a length 64 times or more the external diameter of the screws, mixing the particles within the extruder, which is kept at a temperature comprised between 35 and 350�C, due to the screw rotation at a speed comprised between 15 and 300 rpm; and obtaining an extruded product formed by de-vulcanized rubber. Claims (OCR text may contain errors) 1.

Process for recycling and de-vulcanizing vulcanized rubber, comprising the steps of: - grinding said rubber in a mill in order to shred it into particles having a size substantially comprised between 5 and 15 mm, - introducing said particles in an initial section of a two-screw co-rotating extruder having a length 64 times or more the external diameter of the screws, - mixing said particles within the extruder, which is kept at a temperature comprised between 35 and 350�C, due to the screw rotation at a speed comprised between 15 and 300 rpm, and - obtaining an extruded product formed by de-vulcanized rubber. 2. Process according to claim 1 , wherein water is introduced into said extruder in at least one section located at a distance of at least 48 times the external diameter of the screws downstream of said initial section. 3. Process according to claim 1 or 2, wherein said extruder is provided with means for expelling gases and/or vapours formed inside. 4. Process according to any one of the previous claims, wherein said screws rotate at a speed comprised between 15 and 150 rpm. 5.

Process according to any one of the previous claims, wherein said extruder has a length comprised between 64 and 80 times the external diameter of the screws. 6. Process according to any one of the previous claims, wherein the mechanical power supplied by the main motor of the extruder to the vulcanized rubber treated therein is comprised between 0.1 and 0.4 k W/kg of de-vulcanized rubber produced. 7. Process according to any one of the previous claims, wherein other substances, such as thermoplastic materials or process additives, do not have to be added to said vulcanized rubber before it is subjected to said process steps. 8. Process according to any one of the previous claims, wherein said vulcanized rubber is shred into particles having a size substantially comprised between 10 and 15 mm. Description (OCR text may contain errors) Process for recycling and de-vulcanizing rubber The present invention relates to a process for recycling and de-vulcanizing rubber, constituted in particular by industrial manufacturing rejects and/or by articles which have reached the end of their useful life cycle and originate from specialist collection centres and/or landfill sites.

The molecular chains of vulcanized rubber are typically linked by means of chemical bonds which evolve across bridges of sulphur atoms, which link them transversely. The vulcanized rubber therefore has a structure which is analogous to that of a thermosetting polymer, and thereby cannot be reused as such in the productive cycle. Therefore, a recycling process has to make it possible to break the chemical bonds created by the sulphur, in such a manner that the elastomeric material returns to the original physical/chemical state prior to the vulcanization treatment and is ready to be reused in the productive cycle. Many de-vulcanization processes, both continuous and batchwise, have already been proposed, in which the energy required to break the bonds created by the sulphur is supplied in thermal, mechanical, acoustic (ultrasound) and/or electromagnetic (microwave) form, sometimes also making use of chemical additives.

Mohammad Karrabi et al., "A Study of EPDM Devulcanization in a Co-rotating Twin- screw Extruder", Iranian Polymer Journal 16(5), 2007, 327-335 describes a process for de- vulcanizing a specific rubber - that is EPDM - in a two-screw co-rotating extruder having an L/D ratio of 40. This study links the effectiveness of the results, relating solely to the de- vulcanization of a specific rubber, EPDM, merely to the content of de-vulcanization agent, to the speed of rotation of the screws and to the process temperature, without even mentioning the possibility of treating rubbers of differing nature.

US-2009/0082475 describes a process for de-vulcanizing rubber in a two-screw co-rotating extruder, in which a thermoplastic polymer has to be added to particles of rubber having a size comprised between 150 microns and 5 mm and said particles have to be treated in an extruder having an L/D ratio of 24-60, preferably 32-48, with the screws which rotate at a speed comprised between 300 and 1600 rpm, preferably between 800 and 1000 rpm. The extruded de-vulcanized product is then cooled with water. JP-2002 337 213 describes a process for de-vulcanizing rubber in a two-screw extruder having an L/D ratio of 52.5. JP-6 210 633 describes a process for de-vulcanizing rubber in a one-screw extruder.

The known processes have a number of disadvantages owing to their specificity, which allows only certain types of vulcanized elastomeric material to be treated, to the high consumption of energy per unit of de-vulcanized material produced and to the associated high degree of wear to the machinery used, as well as to the fact that they produce a de- vulcanized rubber with a very strong and acrid smell, which has a strong influence on the possibilities for reuse. It is therefore an object of the present invention to provide a process which is free of the disadvantages mentioned above.

According to the invention, this object is achieved by a process for recycling and de- vulcanizing vulcanized rubber, comprising the steps of: - grinding said rubber in a mill in order to shred it into particles having a size substantially comprised between 5 and 15 mm (the extreme values of the range possibly being excluded), - introducing said particles in an initial section of a two-screw co-rotating extruder having a length 64 times or more the external diameter of the screws, - mixing said particles within the extruder, which is kept at a temperature comprised between 35 and 350�C, due to the screw rotation at a speed comprised between 15 and 300 rpm (the extreme values of the range possibly being excluded), and - obtaining an extruded product formed by de-vulcanized rubber.

The process of the invention is very flexible in terms of the starting materials to be treated and, in principle, makes it possible to de-vulcanize all types of vulcanized rubber or mixtures thereof, such as for example natural rubber (NR.), butadiene rubber (BR), ethylene propylene rubber (EPR), styrene butadiene rubber (SBR), nitrile rubber (NBR), ethylene propylene diene monomer rubber (EPDM), isoprene rubber (IR) and chloroprene rubber (CR). In addition, other substances, such as thermoplastic materials or process additives, do not have to be added to said rubbers, and this results in a reduction in the process costs as well as in the environmental impact connected to the use thereof. The extruder which can be used in the process of the invention is of conventional type and is provided, for example, with screws equipped with mixing elements, which have a reduced external profile, as described in EP-1 136 228 Bl , and which make it possible to control the shearing stresses imparted on the material being manufactured and thus the specific energy absorbed by the latter.

On the whole, the process of the invention makes it possible to break the sulphur bridges present between the chains of the rubber without degrading the latter, owing to the gradual administration of both thermal energy - on account of the heating of the extruder cylinder - and mechanical energy - on account of the shearing stress exerted by the rotating screws - to the particulate material having the granulometry mentioned above. It should be noted that the particles of vulcanized rubber can be both regular and irregular, as long as the maximum size thereof, in particular the diameter if spherical particles are involved, is comprised between 5 and 15 mm, and preferably between 10 and 15 mm (the extreme values of these ranges possibly being excluded). The possibility to use particles of this size bestows an important technological advantage on the process of the invention, because the reduction in the size thereof conventionally carried out by grinding in mills or similar known apparatuses requires a significant expenditure of energy.

By way of example, the reduction of a particle size from 15 to 5 mm requires a specific power of about 0.045 kW/kg and the subsequent reduction from 5 mm into powder - which is usually carried out in a second pass - requires a specific power of about 0.16 kW/kg. The process of the invention is particularly advantageous in terms of the energy balance, since the mechanical power supplied by the main motor of the extruder to the vulcanized rubber treated therein is comprised between 0.1 and 0.4 kW/kg of de-vulcanized rubber produced. By comparison, the corresponding values for conventional processes carried out in two-screw extruders are of the order of 0.6-0.8 kW/kg. In preferred embodiments of the invention, water is introduced into at least one section of the extruder located at a distance of at least 48 times the external diameter of the screws downstream of the initial section, and in addition the gases formed inside the extruder are sucked out by degassing means, in particular extraction openings provided, for example, with mechanical valves.

The latter maintain a constant overpressure inside the extruder and make it possible to expel gases and/or vapours formed during the de-vulcanization process to the outside. The use of the latter devices makes it possible to lessen the smell of the extruded final product, the quality of which is thereby further increased and provides a substantially unlimited range of possibilities for reuse. Again preferably, the extruder can have a length comprised between 64 and 80 times the external diameter of the screws, which are made to rotate at a speed comprised between 15 and 150 rpm. Further advantages and features of the present invention will become evident from the following, non-limiting exemplary embodiment. Scraps of vulcanized rubber of the EPDM type, obtained from articles which are rejected and/or have reached the end of their useful life, are shredded in a mill until particles having a size comprised between 5 and 15 mm are obtained. These particles are loaded into a two- screw extruder of the co-rotating and inter-penetrating type, having a length 64 times the diameter of the screws.

The extruder is kept at a temperature of about 270�C, and the screws are made to rotate in the same direction at a speed of about 150 rpm. A product formed by de-vulcanized rubber, which was supplied with a specific mechanical power of the order of 0.25 kW/kg by the main motor of the extruder during the treatment, is extruded from the extruder. The features of the extruded product are substantially similar to those of the virgin rubber before it was vulcanized; in particular, the Mooney viscosity thereof differs at most by � 5% with respect to that of the virgin starting rubber. The extruded product can be mixed with virgin rubber and subjected to a new vulcanization cycle, advantageously in a quantity comprised between 30 and 50 parts per 100 parts in weight of the mixture. Clearly, without departing from the principle of the invention, the details of construction and the embodiments may differ considerably from those described purely by way of example, without thereby departing from the scope of the invention. Classifications

Question: Which element is added to rubber in the vulcanization process?
Answer: Sulphur